Magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density and has recently demonstrated densities of 612 Gbits/in2. Well-isolated smaller grains of higher magnetic anisotropy constant (Ku) can reduce media noise and improve thermal stability of a magnetic recording layer to achieve these higher areal densities. Enhanced grain isolation in a bottom magnetic recording layer of a PMR media structure, for example, can provide a smaller magnetic cluster size and narrow the size distribution. While microstructure can be improved by controlling oxide content in a recording layer (e.g., bottom magnetic recording layer), the oxide content is a complex function of oxide material of a sputtering target, amount of oxide material in the target, and degree of reactive sputtering with oxygen gas.